Pasteuria ramosa
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Pasteuria ramosa spores |
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| Metschnikow 1888 |
Pasteuria ramosa is a gram-positive bacterium thatforms endospores . It is a close relative of the Bacillus bacteria. P. ramosa is an obligatory parasite of Daphnia magna . The virulence of the bacteria is very high.
description
The endospores are not mobile. They are located in the sediment of the ponds or are freely floating in the water. The size of the endospores is about 5–6 µm. P. ramosa occurs in Eurasia and North America.
P. ramosa is only active in the host . Outside the host, the spores remain in a dormant state in which they can survive in the environment for decades.
Life cycle
The life cycle of P. ramosa begins when D. magna filters the endospores along with the food . A few minutes after ingesting the spores, they are activated and change shape. The exosporium (the outermost layer of the mature spores) opens and reveals the spore envelope. In this step the spore forms a sombrero-like structure. The trigger for the activation is still unknown. After the activation of the spores, the spore adheres to the esophagus . The attachment is very stable, food that passes by cannot tear this attachment off. Without this attachment there can be no infection.
In the next step, P. ramosa enters the body cavity by penetrating the host . Only the bacterial cells get into the body cavity, the rest of the spore remains outside. This step takes about 12 hours. If D. magna sheds its skin within these 12 hours, not only does the carapace fall off, but also the attached spore.
After the bacterium has established itself in the body cavity, it begins to multiply and goes through various stages of development. The vegetative stages can be visible in the hemolymph after about 8 days .
About 5 to 15 days after infection, D. magna is castrated and can no longer reproduce. The cauliflower stage is visible after approx. 12 days. The first spores are visible 20 days after the primary infection . Fully mature spores are only visible in dying or dead D. magna .
After castration, the body size of the D. magna becomes much larger ( gigantism ) than in the case of non-infected. The color of the D. magna also changes. D. magna is no longer transparent, but rather brownish. The host dies 40-50 days after infection and the spores are released into the environment.
The transmission of P. ramosa is only horizontal; vertical transmission has never been observed.
Individual evidence
- ^ A b c D. Ebert: Ecology, Epidemiology, and Evolution of Parasitism in Daphnia. National Library of Medicine (US), National Center for Biotechnology Information, 2005.
- ↑ a b c d D. Ebert, D. Duneau, MD Hall, P. Luijckx, JP Andras, L. Du Pasquier, F. Ben-Ami: A Population Biology Perspective on Stepwise Infection Process of Bacterial Pathogen Pasteuria ramosa in Daphnia. In: Advances in Parasitology. Vol 91, 2016, pp. 265-310.
- ^ A b D. Ebert: Host-parasite coevolution: Insights from the Daphnia-parasite model system. In: Curr Opin Microbiol. 11 (3), Jun 2008, pp. 290-301. doi: 10.1016 / j.mib.2008.05.012 . Review. PMID 18556238
- ↑ D. Ebert, CD Zschokke-Rohringer, HJ Carius: Within - and between-population variation for resistance of Daphnia magna to the bacterial endoparasite Pasteuria ramosa. In: R. Soc. Lond. 265, 1998, pp. 2127-2134.
- ↑ a b c D. Duneau, P. Luijckx, F. Ben-Ami, C. Laforsch, D. Ebert: Resloving the infection process reveals striking differences in the contribution of environment, genetics and phylogeny to host-parasite interactions. In: BMC Biology. 2011.
- ↑ D. Ebert, P. Rainey, TM Embley, D. Scholz: Development, life cycle, ultrastructur and phylogenetic position of Pasteuria ramosa Metchnikoff 1888: ediscovery of an obligate endoparasite of Daphnia magna Straus. In: R. Soc. Lond. 351, 1996, pp. 1689-1701.